package dujiu.luogu.circulation;

import java.util.Scanner;


public class P2669 {
    public static void main(String[] args) {
        // 把工资相同的天当作一个整体，一共有n个整体
        // 并且第n个整体，整体内每一天的单日工资都为n
        Scanner sc = new Scanner(System.in);
        int k = sc.nextInt();
        int n = 1;
        int total_salary = 0;
        // 当前天数
        int i = 1;
        while (i<=k){
            if (k - i >= n){
                total_salary = total_salary + n*n;
                i = i + n;
            }else {
                total_salary = total_salary + (k -i+1)*n;
                i = k+1;
            }
            n++;
        }
        System.out.println(total_salary);
    }
}


















